The present invention relates to a constant speed holding device for allowing a vehicle to run automatically at a constant speed.
In recent years, it has become popular to equip automobiles with a constant speed holding device for automatically controlling a running speed of the automobile at a constant value preset under normal running conditions.
An example of such a device is shown in Japanese Patent Application Laid-open No. 98636/1983, in which a desired speed is set when it is attained, and the set value is used as an aimed speed subsequently. That is, a signal corresponding to a deviation between an actual running speed and the aimed speed is obtained, and, after a predetermined gain is given to the deviation signal, it is operated with an acceleration signal having a predetermined gain given thereto to provide a signal to an actuator of a throttle of an engine of the automobile to make the actual running speed closer to the aimed speed. The device further has a function of allowing the constant speed of the automobile to be recovered after the constant running speed is cancelled temporarily.
In the conventional device mentioned above, however, the recovery of the aimed speed must be done by accelerating the automobile under an acceleration control such that an acceleration becomes a predetermined value. As is well known, an actual acceleration during uphill running, for example, is smaller than the predetermined acceleration, and therefore a throttle is opened to a value beyond a value necessary to attain the desired acceleration during normal running. Consequently, it takes a long time to close the throttle to the necessary value by an actuator thereof, resulting in a problem of over compensating for the acceleration.